Probably not. By the time it gets to a courtroom they'll almost certainly have a lot more than just MAC addresses, so while the bomber might plead "some jackass spoofed my MAC address to frame me", that wouldn't explain his purchase history, the explosives residue around his home and clothing, etc.
A MAC address doesn't prove anything, but courtrooms aren't about proof. They're evidence, not proof, and enough evidence is all the German prosecution should need to have a relatively easy time in court.
I'm certainly no legal expert, but wouldn't the whole "fruit of the poisonous tree" argument apply to any evidence found after and/or as a result of the MAC address connection?
Second, that applies to illegally obtained evidence. For example, if (in the US) the police tortured someone/broke in somewhere without a search warrant to obtain the MAC, then the fruit of the poisonous tree doctrine would likely apply to the evidence found as a result of the MAC address connection.
Finding additional evidence starting from a vague lead ("the robber was wearing black clothes") is not something illegal, it's good police work.
If the cops get a search warrant for an address and it turns out that the bad guy lived next door, but the real occupants are running a meth lab, there's no doctrine anywhere that would suppress the evidence they find. As long as it's an honest mistake there's no problem.
In addition, the concept only pertains to information acquired through unconstitutional means, such as not having a warrant to search. Getting incorrect information is not unconstitutional and investigators rely on much more than a single piece of information when building a case.
Edit: by unconstitutional I’m speaking of the US. I am not sure what constitutional protections apply to other country’s citizens, but assume they may be similar.
There definitely is, just not using that name. In Germany, it’s an explicit law.
It just doesn’t apply in this case, because it hinges on bad faith. Incidental evidence found while following some other legitimate trails is admissible.
IIRC, it's barely a concept in English law, primarily US law.
It has however seen some use in the ECHR , notably against Germany (citing various US court cases):
> the applicant sought a declaration that [...] all items of evidence[...], which had become known to the investigation authorities because of the confession extracted – the so-called “fruit of the poisonous tree” – was prohibited [...] The Chamber considered that there was a strong presumption that the use of items of evidence obtained as the fruit of a confession extracted by means contrary to Article 3 rendered a trial as a whole unfair in the same way as the use of the extracted confession itself.
